A new approach to creating an ancient tree of life
Researchers trace lineages of microbes to help in understanding the evolutionary history of key microorganisms in the ocean.
A new approach to creating a microorganism family tree may provide new insights into the changing tides of the future.
Carolina Martinez-Gutierrez and Frank Aylward have created a genetic tree that establishes a timeline for when 13 clades – the lineages of bacteria and archaea – colonized in the ocean. Recently published in elifesciences.org, this novel molecular dating provides insights into how life evolved in the ocean.
“Looking into the evolutionary history of relevant marine microbial clades can help us predict potential future scenarios in the ocean,” said Carolina Martinez-Gutierrez, who recently completed her Ph.D. in biological sciences at Virginia Tech.
Ancient marine microbes
The lineages of these microorganisms, called clades, play a vital role in the biogeochemical cycles that govern the environmental health of the planet, and they are still abundant in diverse zones of waters.
“These clades are extremely ancient,” said Martinez-Gutierrez, who's currently working as a postdoctoral fellow at North Carolina State University. “Their diversification spans 2 billion years, which is an enormous amount of time if you consider the earth is about 4.2 billion years old and life is about 3.8 billion years old.”
The oldest clades, according to their findings, diversified around the time of the Great Oxidation Event — 2.4 billion years ago — when oxygen concentrations in the ocean increased yet remained low. These groups remain prevalent in regions of the ocean called oxygen-minimum water zones today.
The diversification of the youngest clades occurred at or after 800 million years ago, after the Proterozoic Oxidation Event, which brought a further increase in oxygen in the atmosphere and ocean. The lineages of these clades are still abundant in oligotrophic waters, which are poor in nutrients.
Effects of climate change
“Think of the oxygen minimum zones as an ancient environment and the oligotrophic waters as a more recently emerging environment. Interestingly, both are expanding as climate change progresses,” said Frank Aylward, associate professor of biological sciences in the College of Science.
Climate change is expected to drive the expansion of oligotrophic regions due to warmer atmospheric temperatures as well as warmer water temperatures. As the water warms, stratification of the ocean increases and nutrient rich waters from the deep ocean do not reach the surface.
“I like this whole idea of refugia, which in this case are these oxygen minimum zones,” said Aylward, affiliate faculty with the Global Change Center and the Center for Emerging Zoonotic and Arthropod-borne Pathogens, which are part of the Fralin Life Sciences Institute. “They are like a refuge for these ancient lineages that have evolved at a time when oxygen wasn’t very abundant, and they could still thrive in these environments.”
Why the past matters
Discovering the geochemical conditions under which the clades of bacteria and archaea first diversified provides context for understanding the impact of climate changes in marine ecology and clues to how future climate shifts may impact its biogeochemical cycles. These cycles regulate nitrogen, carbon, and oxygen levels in the atmosphere as well as waters; therefore, these marine microbes have a central role in shaping the biogeochemistry of the planet.
As part of the biogeochemical cycles of the oceanic ecosystem, marine bacteria and archaea break down complex carbon-based compounds, which ultimately releases carbon dioxide. So it is noteworthy that the researchers found numerous genes involved in the metabolism of carbon and other essential nutrients in the genetic traits of clades gained during the colonization of the ocean.
“I would argue that it is really important to know the evolutionary history of organisms in an ecosystem in order to know how the ecosystem functions; it is relevant foundational information,” said Aylward, who is also an affiliated faculty with the Molecular, Cellular, Biology Graduate Program.
Going forward, Martinez-Gutierrez will continue this research as an assistant professor in the earth science department at the University of California, Santa Barbara, while Aylward will continue to study diverse aspects of microbial diversity.
